[@Polaris North] You can either go for something mild or massive. KimmiNinja's character seems like she's staring blankly into space since she's interacting with her quirk, who kinda sentient. WXer's character was just shaking. Story-wise, your character would find it difficult to find out what his ability is. 

You could go with suddenly creating portals out of nowhere and he wouldn't know what it was. Or maybe just having some weird epiphany?